U.S. Pat. No. 5,396,247 (JP 3064644), for example, discloses an A/D converter circuit for converting an analog voltage signal input to an input signal line into a binary digital data and outputting it to an output data line. In this A/D converter circuit, a plurality of inverting circuits are connected in a ring form to form a pulse circulating circuit, and an input voltage which is an analog input is applied as a power supply voltage to each of the inverting circuits to convert the input voltage into a digital data by utilizing the fact that an inverting operation time of the inverting circuits varies depending upon the power supply voltage.
In the A/D converter circuit of this type, however, the inverting circuit of which the inverting operation time varies depending upon the power supply voltage is formed by semiconductors such as MOS transistors; i.e., the inverting operation time varies depending upon the temperature due to its characteristics. Therefore, a data value output being converted into a digital data based on an input voltage input as a power supply voltage to the inverting circuit is subject to vary depending also upon a change in the ambient temperature.
U.S. Pat. No. 6,891,491 (JP 2004-274157A) discloses a method of correcting non-linearity and an apparatus for correcting non-linearity of the A/D-converted output data. According to this correction method, an approximated straight line or curve is calculated or corrected relying upon a digital operation to suppress variation in the digital data caused by the ambient temperature.
According to this correction method, however, it is necessary to repeat a predetermined arithmetic operation for every A/D conversion to digitally operate the approximated straight line or curve. Therefore, even if a variation in the digital data caused by the ambient temperature can be suppressed, the scale of the arithmetic processing circuit increases and, besides, an extended period of time is required for the complicated operation that occurs repetitively. Thus, this technology is not suited for high-speed A/D conversion processing.
The above problem can be technically solved by utilizing a GaAs device capable of executing the arithmetic operation at high speeds for the arithmetic processing circuit. However, the cost of the GaAs device itself and the presence of the pulse circulating circuit that does not require high-speed processing necessitate a new step in the process for producing the semiconductors and increases costs of production.